I have spent some time looking at this. It is from a large animal. It has a ball at one end which makes it a humerus or a femur. It is wide and flat, like a paddle, so it is from an aquatic animal. The bone structure is a little odd and on the end opposite the ball the bone fades into cartiladge, this is a feature of reptiles. (although a simillar feature can be found in young cetacea). On balance I think it is the humerus of a leatherback turtle